The invention relates to a method for controlling the temperature of edible dough during a kneading step in the making process of bread, confectionery and the like, and to an apparatus used in the above method.
During the kneading step, it is necessary to mix and knead powder materials such as wheat flour and starch with liquid materials such as water and liquid egg and/or additives such as sugar and salts. This kneading step is usually carried out by means of a mixer or a kneader in an industrial scale. The mixer is composed of a bowl for receiving materials (called also a xe2x80x9cdough bowlxe2x80x9d) and a stirring blade or an impeller for mixing and stirring. There are manufactured many types and structures of the mixer, which are selected and used depending on the properties of products to be prepared.
It is often necessary to control the temperature of dough under kneading in order to equalize and maintain the quality of final products at a certain level, by cooling it down for preventing the overheating due to its friction and hydration, or by heating it for minimizing the effects on the quality of the products due to the fluctuation in the temperature of the materials. Especially, when the dough is kneaded along with its proofing, a strict temperature control is required since the dough temperature will seriously affect the yeast""s activity.
The period of time for kneading is important as well. It is well known that the properties of dough such as texture will be affected by the period of time for kneading even if the kneading conditions such as the dough temperature and the stirring strength are kept constantly. As the dough temperature changes, an optimum period of time for kneading will of course have to be changed as well. The change of said time has conventionally been handled by those skilled in the art who are experienced in doing this procedure. However, when the edible dough is produced in a large scale, it will be difficult to change the period of time for kneading depending on the dough temperature according to their experience. Furthermore, the change of the time for kneading in the production of the same item would cause a serious problem in view of a production schedule. Therefore, it is important to control the dough temperature during the kneading step in order to maintain the kneading time, as well.
Japanese Patent Application laid open Sho.61 (1986)-88834 and Japanese Patent Application laid open Sho.59 (1984)-198928 disclose methods for controlling the temperature of edible dough during kneading. In said methods, liquid heating media such as water and antifreezing solution are used to control the dough temperature through the surface of a wall of the dough bowl. As a result, an apparatus for controlling the temperature of the liquid heating media and a thermometer have to be attached to the dough bowl, which will impose a lot of limitation on the structure of the mixer. Those methods have been therefore actually applied only to a particular type of the mixer.
In the method disclosed in Japanese Patent Application laid open Sho.54 (1979)-119051, dry ice is added into the dough under kneading to cool it by heat of sublimation. Although there is no limitation in the structure of the mixer in this method, the scatter of the dry ice to surroundings will seriously affect the working environments. As a result, other devices will have to be installed as a countermeasure against shortage of oxygen gas for the workers in order to improve the working environments.
The French patent application (FR2443206A) discloses a method for controlling the dough temperature using gas such as air, in which a mixer is equipped with a series of temperature-controlling apparatuses (gas-generating apparatuses) that project the gas on to the dough. The apparatuses may be used in any kind of the mixer. However, since humidity of the gas is not controlled, it will be hard to keep the water content in the dough, and the quality or homogeneity of the dough may deteriorate.
The method disclosed in the above French patent application further has the following problems to be solved:
(1) Since it takes some time for the gas to reach a predetermined temperature from the start of controlling the dough temperature, it will be difficult to control the dough temperature in case it changes drastically;
(2) Since the gas (air) is discharged into the surroundings after having been projected on to the dough, heat can not be recovered and the cost for the temperature controlling will become relatively high;
(3) The diffusion of the gas around the mixer will adversely affect the working environments in the surroundings, changing a room temperature, for example; and
(4) The temperature-controlling apparatus has to be stopped at a regular interval for defrosting it during a cooling operation, which will make it difficult to operate it for a long period of time.
The purpose of the present invention is therefore to provide a method for controlling the temperature of edible dough under kneading without causing the above problems, and an apparatus that may be used in the above method.
The present inventors have found that it is possible to control the dough temperature by means of the gas such as air without providing the mixer with a special temperature-controlling apparatus. The present invention may be applied to any kind of the mixer.
The present invention relates to a method for controlling the temperature of edible dough during a kneading step, comprising introducing a controlled amount of gas having a controlled temperature and humidity (referred to hereinafter also as the xe2x80x9ctemperature-controlling gasxe2x80x9d) into a mixer.
The present invention also relates to an apparatus for controlling the temperature of edible dough that may be used in the present method. The present apparatus comprises an air conditioner that is capable of introducing the controlled amount of gas having a controlled temperature and humidity into the mixer. The present invention further relates to an apparatus for mixing edible dough, comprising the above apparatus for controlling the temperature of edible dough and the mixer. One of its examples is shown in FIG. 1.
In controlling the temperature of edible dough by means of the gas such as air, the humidity of the gas is essential in addition to heat-exchange properties such as its temperature and velocity. The temperature and velocity of the gas will seriously affect the efficiency of controlling the dough temperature. On the other hand, the humidity of the gas will seriously affect the quality of the dough. For example, in case the gas with a relatively low humidity is projected on the edible dough having a high water content, the water content of the dough will be reduced and its quality will deteriorate.
In the present invention, the gas to be used is controlled with respect to not only its temperature but also its humidity so that the quality of the resulting dough may be kept at a constant level. The temperature, velocity and humidity of the gas may be optionally selected by those skilled in the art, depending on the kind and amount of the edible dough, and the conditions during the kneading such as the capacity and operating conditions of the mixer, and a surrounding temperature.
When the edible dough suddenly generates heat during the kneading step, air at a low temperature shall be promptly projected on the surface of the dough and keep its temperature below a certain level in order to control the quality of the dough. However, if the temperature of gas such as air is tried to control just after it has been detected, it will be impossible to respond to a sudden change of the dough temperature.
It is therefore preferable in the present invention that the gas such as air has been prepared and kept in advance at a predetermined temperature and humidity by means of the air conditioner that was started simultaneously with the mixer, and the thus prepared gas is circulated through pipelines without being introduced into the mixer. On demand, the lines are switched by means of a damper, for example, so that the thus controlled gas may be instantly introduced into the mixer. In the present invention, the temperature of the edible dough is maintained at a constant level by rapidly controlling it in response to its sudden change, so that the quality of the final edible dough may be maintained at a desired and constant level.
If the gas or air used in the temperature controlling is discharged into the surroundings, heat can not be recovered and the cost for the temperature controlling will become relatively high.
Accordingly, it is preferable in the present invention to introduce the gas into the air conditioner again without discharging it out of a system, thus to circulate and re-use the gas. As a result, it is possible in the present invention to recover the heat and to reduce the cost for the temperature controlling.
Since the mixing of the edible dough is usually done at a place where people work, the working environments around the apparatuses should be especially taken into consideration. According to the present invention, since the gas used for the temperature controlling is circulated for re-use and is substantially not discharged into the surroundings, the risk of diversely affecting the working environments will be reduced significantly.
The quality of bread and confectionery will deteriorate as time passes away. On the other hand, consumers now strongly require fresh or just-prepared products. As a result, more factories producing such products recently tend to be run around the clock in order to produce the products as frequently as possible. There is no problem with the mixer per se for a 24-hour continuous running. However, it will be necessary to defrost an air-cooling part of the air conditioner at a regular interval to remove the ice accumulated in that part when cooling gas is provided by the air conditioner. Since the air conditioner can not be used during the defrosting procedure, the temperature of the mixer can not be controlled during the defrosting, either. Accordingly, it is preferable in the present invention to use two or more air conditioners so that they can be continuously run around the clock by optionally switching them by means of the damper.